The present invention is directed to integrated circuits and, more particularly, to a voltage level shifter.
Semiconductor devices often have more than one direct current (DC) power supply voltage domain. Such devices include a primary source of DC power, which may be a battery, a DC-DC converter for providing a secondary power supply at a different voltage, a DC-DC control module for controlling the DC-DC converter, and a power management controller for managing powering-up, powering-down, standby and sleep of the device, for example.
Voltage level shifters are used as interfaces between the different voltage domains. A level shifter converts the voltage level of an asserted signal from an originating voltage domain to a voltage suitable for the destination voltage domain. The voltage level of de-asserted signals is typically the same (e.g., ground). A complex semiconductor device such as a system on a chip (SoC) may have many level shifters. It is important that the power consumption and leakage current of the level shifters be reduced.
Level shifters are often used in applications, such as battery powered devices, where the steady voltage of the primary power supply varies. The reliability and predictability of powering-up of the power supply for each domain are also concerns. In a conventional level shifter, a detector may be added in the domain of the primary power supply to detect if a secondary power supply of another domain has attained the start-up target voltage. However, including such a detector increases circuit area, consumes more power, and degrades the efficiency of DC-DC conversion, especially in low power mode.
It would be advantageous to have a voltage level shifter having low leakage current without needing an isolation signal, and having reliable powering-up of the power supply and a well-controlled output voltage even with a big range of primary power supply voltage.